Preheat oven to 400F. Brush 6 4-in. ramekins with butter and dust with 1 tbsp granulated sugar. Divide blueberries among ramekins. Place ramekins on a baking sheet.
Whisk eggs until frothy in a medium bowl. Whisk in 1/4 cup sugar, cream, milk and liqueur. Gently whisk in flour until just combined. Do not overmix. Scrape batter evenly over berries.
Bake in centre of oven until set but jiggly when gently shaken, about 20 min. Let stand 10 min. Serve warm, dusted with icing sugar.

Use a 9-in. glass pie plate instead of individual ramekins. Bake uncovered, 20 min. Cover with foil and continue baking until set but jiggly when gently shaken, 10 to 15 more min.